US7224349B2 - Electronic apparatus - Google Patents

Electronic apparatus Download PDF

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Publication number
US7224349B2
US7224349B2 US10/457,767 US45776703A US7224349B2 US 7224349 B2 US7224349 B2 US 7224349B2 US 45776703 A US45776703 A US 45776703A US 7224349 B2 US7224349 B2 US 7224349B2
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Prior art keywords
clock
spread spectrum
spread
clocks
ics
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US10/457,767
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US20040041775A1 (en
Inventor
Michio Irie
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Seiko Epson Corp
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Seiko Epson Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K4/00—Generating pulses having essentially a finite slope or stepped portions
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/18—Timing circuits for raster scan displays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/713—Spread spectrum techniques using frequency hopping
    • H04B1/715—Interference-related aspects
    • H04B2001/7152—Interference-related aspects with means for suppressing interference

Definitions

  • the present invention relates to decreasing EMI noise that electronic apparatuses generate.
  • EMI noise Noise generated by various types of electronic apparatuses may cause undesirable interferences (EMI(Electromagnetic Interference)) against other electronic apparatuses.
  • EMI noise Various types of regulations are therefore stipulated for the noise (hereinafter “EMI noise”) generated by the electronic apparatuses.
  • manufacturers may intend to decrease the EMI noise generated by the electronic apparatuses so that the electronic apparatuses to be manufactured meet EMI noise regulations.
  • FIG. 3 is a schematic showing an exemplary frequency spectrum of a clock.
  • the frequency spectrum of the clock usually has the peaks of the amplitudes at the oscillation frequency (fundamental wave: f 1 ) of the clock and the frequencies (f 2 , f 3 , . . . ) corresponding to each of its harmonics.
  • This causes the frequency spectrum of the EMI noise occurring in the electronic apparatus as well to generally have the peaks of the amplitudes at the oscillation frequency of the clock (f 1 ) and the frequency (f 2 , f 3 , . . . ) corresponding to each of its harmonics.
  • the peaks of the amplitudes occurring at each of the frequencies of the fundamental wave and its harmonics are required to be decreased.
  • the frequency spectrum is spread to decrease the peaks of the amplitudes of the frequency spectrum generated at the frequencies of the fundamental wave (f 1 ) and its harmonics (f 2 , f 3 . . . ) of the clock.
  • varying the oscillation frequency of the clock to spread the frequency spectrum is referred to as “spread spectrum”.
  • the amount of variation in the oscillation frequency of the clock is referred to as “spread amount”.
  • the present invention addresses or solves the above and/or other problems, and provides the ability to efficiently decrease EMI noise as the entirety of the electronic apparatus where there is a plurality of types of clocks that are used as the references for the operations in the electronic apparatus.
  • a first exemplary electronic apparatus of the present invention operates based on a plurality of types of clocks including a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the electronic apparatus includes a plurality of ICs using the clocks as references for the operations, and at least the clock used by the largest number of ICs is the spread spectrum clock from among the plurality of types of clocks.
  • the clock that is employed by the largest number of ICs by using as the spread spectrum clock the clock that is employed by the largest number of ICs, all of the EMI noise generated by at least these ICs can be decreased.
  • the EMI noise occurring as the entirety of the electronic apparatus can be efficiently decreased.
  • a second exemplary electronic apparatus of the present invention operates based on a plurality of types of clocks including a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the electronic apparatus includes a plurality of ICs using the clocks as references for the operations and at least one clock generator generating the clocks, and at least the clock with the longest signal path from the clock generator generating the clock to the IC where the clock is ultimately provided is the spread spectrum clock from among the plurality of types of clocks.
  • a third exemplary electronic apparatus of the present invention operates based on a plurality of types of clocks including a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the clock with the highest frequency is the spread spectrum clock from among the plurality of types of clocks.
  • the clock with the highest frequency as the spread spectrum clock, the energy of the EMI noise occurring as the entirety of the electronic apparatus can be efficiently suppressed, thus realizing decrease in the EMI noise.
  • a fourth exemplary electronic apparatus of the present invention operates based on a plurality of types of clocks including a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the electronic apparatus includes at least one clock generator generating the clocks, and at least the clock with the highest output current from the clock generator is the spread spectrum clock from among the plurality of types of clocks.
  • the clock with the highest output current output from the clock generator as the spread spectrum clock, the energy of the EMI noise occurring as the entirety of the electronic apparatus can be efficiently suppressed.
  • a fifth exemplary electronic apparatus of the present invention operates based on a plurality of types of clocks including a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the electronic apparatus includes at least one clock generator generating the clocks, and at least the clock with the highest driving power voltage of driving the clock generator is the spread spectrum clock from among the plurality of types of clocks.
  • the clock with the highest driving power voltage of driving the clock generator as the spread spectrum clock, in the same manner as in the fourth electronic, the energy of the EMI noise occurring as the entirety of the electronic apparatus can be efficiently suppressed.
  • the at least one clock generator includes at least a first clock generator generating the spread spectrum clock and a second clock generator generating the non-spread spectrum clock.
  • the first clock generator and the second clock generator share the same IC.
  • Such a construction contributes to the reduction or curtailment of the number of parts and the area occupied on the circuitboards.
  • a projector of the present invention includes at least a liquid crystal panel and operating based on a plurality of types of clocks having a spread spectrum clock whose frequency spectrum is spread and a non-spread spectrum clock whose frequency spectrum is not spread.
  • the clock ultimately provided to the liquid crystal panel is the spread spectrum clock from among the plurality of types of clocks.
  • the clock ultimately provided to the liquid crystal panel that is, the display clock normally corresponds to the clock used by the largest number of ICs and corresponds to the clock that has the longest signal path from the clock generator to the IC where the clock is ultimately provided.
  • the present invention is not limited to a mode or the exemplary embodiments of the apparatus invention of the above electronic apparatuses, such as the liquid crystal projector.
  • the present invention can be realized as a method, such as a spread spectrum clock selection method, for example.
  • FIG. 1 is a schematic of a liquid crystal projector to which the present invention is applied.
  • FIG. 2 is a schematic showing one example in which a clock generator generating a non-spread spectrum clock and a clock generator generating a spread spectrum clock are constructed using the same IC.
  • FIG. 3 is a schematic showing an exemplary frequency spectrum of a clock.
  • liquid crystal projector which is one of the exemplary electronic apparatuses to which the invention can be applied.
  • FIG. 1 is a schematic showing the construction of a liquid crystal projector to which the present invention is applied.
  • a liquid crystal projector 100 shown in FIG. 1 is provided primarily with an input interface 102 , an image processor 104 , a panel controller 106 , a panel driver 108 , a liquid crystal panel 110 , a system controller 112 , a USB (Universal Serial Bus) controller 114 , a 130 MHz non-spread spectrum clock generator 116 , a 75 MHz spread spectrum clock generator 118 , and a 50 MHz non-spread spectrum clock generator 120 , any of which is constructed using an independent IC (Integrated Circuit).
  • the image processor 104 has a frame memory controller 105 inside.
  • the input interface 102 when the signal is an analog signal, A/D conversion is performed on an input image signal, which is fed to the image processor 104 ; when the signal is a digital signal, the signal is converted into the signal with a format that can be provided to the image processor 104 and then is fed to the image processor 104 .
  • the image processor 104 in accordance with control of the frame memory controller 105 , the input image signal is written in frame memory (not shown) and the written image signal is read. In the processes of these writing and reading, various image processing is performed.
  • the panel controller 106 controls the panel driver 108 that drives, in accordance with the control, the liquid crystal panel 110 , where light radiated from an illumination optical system (not shown) in response to the drive is modulated in accordance with the image signal.
  • the modulated light is projected on a screen (not shown) by a projection optical system, so that an image is displayed on the screen.
  • the system controller 112 controls the input interface 102 and the USB controller 114 .
  • the USB controller 114 causes a control signal or the like to be fed to a USB port (not shown) from other electronic apparatuses connected thereto and vice versa.
  • a memory clock 122 which is a 130 MHz clock
  • the memory clock 122 is generated at the 130 MHz non-spread spectrum clock generator 116 to be used as reference for only the operation of the frame memory controller 105 in the image processor 104 .
  • the display clock 124 which is a 75 MHz clock, is generated at the 75 MHz spread spectrum clock generator 118 to be used as reference for the operations of the circuit part in the image processor 104 except the frame memory controller 105 , the panel controller 106 , the panel driver 108 , and the liquid crystal panel 110 .
  • the system clock 126 which is a 50 MHz clock, is generated at the 50 MHz non-spread spectrum clock generator 120 to be used as the reference for the operations of the input interface 102 , the system controller 112 and the USB controller 114 .
  • the display clock 124 is used by each of the ICs of the image processor 104 , the panel controller 106 , the panel driver 108 , and the liquid crystal panel 110 , the number of which ICs is largest compared to those of the other clocks. Since the EMI noise generally occurs from the ICs using the clock, as the number of ICs using the clock increases, the amount of EMI noise caused by the clock increases.
  • the spread spectrum is therefore applied to such a clock used by the largest number of ICs, that is, the display clock 124 .
  • a device which serves to output the clock (hereinafter “spread spectrum clock”) whose frequency spectrum is spread by varying the oscillation frequency of the clock as the 75 MHz spread spectrum clock generator 118 generating the display clock 124 , so that the display clock 124 is generated as the spread spectrum clock.
  • the memory clock 122 is used by only the frame memory controller 105 in the image processor 104 , the number of ICs using the memory clock 122 is only one, allowing the amount of EMI noise caused by the memory clock 122 to be small. This allows the memory clock 122 not to undergo the spread spectrum.
  • a device which serves to output a clock having practically a single frequency (hereinafter “non-spread spectrum clock”) as the 130 MHz non-spread spectrum clock generator 116 generating the memory clock 122 , so that the memory clock 122 is generated as the non-spread spectrum clock.
  • the system clock 126 is used by each of the ICs, that is, the input interface 102 , the system controller 112 , and the USB controller 114 , the number of which ICs is less than that of the case with the display clock 124 .
  • Employing the spread spectrum clock as one used by the input interface 102 and the USB controller 114 is not desirable because of the following reasons.
  • USB In USB, the specification thereof strictly sets 500 ppm or below as the tolerable range of jitter with respect to a signal. Therefore, when the clock used by the USB controller 114 is spectrum-spread in order to decrease the EMI noise, in some spread amount, there is a possibility that the jitter of a signal may exceed the above tolerable range in the USB controller 114 .
  • the specifications of image signals fed to the liquid crystal projector 100 exist in various types in accordance with various conditions, such as the types of devices (a computer, a DVD player, a video recorder, etc.) outputting the image signals and the resolutions of the images represented by the image signals.
  • the input image signal is analyzed to determine the specification thereof, in accordance with which specification the image signal is processed.
  • a method to determine the specification of the image signal is performed by causing the input interface 102 to find the cycle, the period, the polarity, etc.
  • the input interface 102 counts the cycle and the period of the synchronization signal using a measurement clock generated based on the system clock 126 to measure. Spectrum-spreading the system clock 126 in order to decrease the EMI noise, therefore, leads to spectrum-spread of the measurement clock generated based on the system clock 126 as well.
  • the characteristic value of the synchronization signal to be measured may vary in accordance with variation in the oscillation frequency, which, even though the specification of the actual image signal is not changed, may lead to a determination that the specification of the image signal is changed.
  • the system clock 126 is not spectrum-spread either in the same manner as the memory clock 122 .
  • a device which serves to output the non-spread spectrum clock as the 50 MHz non-spread spectrum clock generator 120 generating the system clock 126 in the same manner as the 130 MHz non-spread spectrum clock generator 116 , so that the system clock 126 is generated as the non-spread spectrum clock.
  • the EMI noise generated by at least these ICs can be decreased by applying the spread spectrum to the display clock 124 that is used by the largest number of ICs, the EMI noise occurring at the entirety of the liquid crystal projector 100 can be efficiently decreased.
  • the display clock 124 is the only clock to which the spread spectrum is applied, the cost to apply the spread spectrum can be greatly decreased.
  • the spread spectrum is therefore applied to the clock used by the largest number of ICs from among plurality of types of clocks.
  • the EMI noise occurs from not only the ICs using the clocks but also from the wires establishing the connections among the ICs to carry the clocks.
  • the spread spectrum is applied to a clock that has the longest signal path from a clock generator generating the clock to an IC where the clock is ultimately provided.
  • the display clock 124 is provided from the 75 MHz spread spectrum clock generator 118 to the liquid crystal panel 110 at the destination thereof via the image processor 104 , the panel controller 106 , and the panel driver 108 , which signal path is longest compared to those of the other clocks.
  • the spread spectrum is applied to the display clock 124 .
  • the spread spectrum to the display clock 124 that has the longest signal path from the clock generator to the IC where the clock is ultimately provided, since not only the EMI noise occurring from the ICs using the display clock 124 but also the EMI noise occurring from the wires establishing the connections among these ICs to carry the display clock 124 can be efficiently decreased totally, the EMI noise occurring from the entirety of liquid crystal projector 100 can be efficiently decreased.
  • the spread spectrum is applied to the clock used by the largest number of ICs among a plurality of types of clocks in the first exemplary embodiment as well as the clock having the longest signal path from the clock generator to the IC where the clock is ultimately provided.
  • the spread spectrum is applied to the clock having the highest frequency.
  • the frequency spectrum of the EMI noise generally has the peaks of the amplitudes at the frequency (f 1 ) of the clock and each of the frequencies (f 2 , f 3 . . . ) corresponding to the harmonics thereof. Accordingly, when there are, for example, the 50 MHz clock and the 100 MHz clock as the clocks, both are compared with respect to a harmonic of 200 MHz. Since 200 MHz is a quadruple of 50 MHz and 100 MHz is a double of 50 MHz, the 100 MHz is lower in terms of the order of the harmonic. Generally, as the order of the harmonic decreases, the energy thereof increases. The energy of the EMI noise caused by the 100 MHz clock is therefore higher than that of the EMI noise caused by the 50 MHz clock with respect to an EMI noise of 200 MHz.
  • the energy of the EMI noise occurring in the liquid crystal projector 100 as a whole can be efficiently decreased, thus realizing a decrease in the EMI noise.
  • the clock is generated by the clock generator.
  • the energy of the clock output from the clock generator usually increases in proportion to the square of the output current output from the clock generator. Since the EMI noise is caused by the clock, the energy of the EMI noise increases in accordance with increase in that of the clock output from the clock generator.
  • the spread spectrum is applied to the clock whose current output from the clock generators is highest.
  • the energy of the EMI noise generated from the liquid crystal projector 100 as a whole can be efficiently decreased, thus realizing decrease in the EMI noise.
  • the energy of the clock output from the clock generator usually increases in accordance with increase in the driving power voltage to drive the clock generator.
  • the energy of the EMI noise increases in accordance with increase in the energy of the clock output from the clock generator.
  • the spread spectrum is applied to the clock whose driving power voltage for driving the clock generator is highest.
  • the energy of the EMI noise generated from the liquid crystal projector 100 as a whole can be efficiently decreased as well, realizing a decrease in the EMI noise.
  • the spread spectrum is applied to only the clock used by the largest number of ICs, which is the display clock 124 , while the spread spectrum is not applied to the other clocks, which are the memory clock 122 and the system clock 126 .
  • the spread spectrum may be applied to, for example, the memory clock 122 other than the display clock 124 . That is, the spread spectrum only has to be applied to at least the clock used by the largest number of ICs where there is a plurality of types of clocks in the electronic apparatus. This is applied to the other embodiments as well.
  • the clock generator 116 or 120 generating the non-spread spectrum clock and the clock generator 118 generating the spread spectrum clock may be constructed using the same IC.
  • FIG. 2 is a schematic that shows one example of a construction in which the clock generator generating the non-spread spectrum clock and the clock generator generating the spread spectrum clock are constructed using the same IC.
  • the three clock generators shown in FIG. 1 are constructed using the same IC.
  • This IC 130 is provided with a crystal oscillator 132 and a frequency synthesizer 134 and is connected to a crystal resonator 136 outside.
  • the crystal oscillator 132 employs the crystal resonator 136 as the inductive impedance to generate a signal having a constant frequency, from which signal the frequency synthesizer 134 generates each of two non-spread spectrum clocks having different frequencies and a spread spectrum clock undergoing the spread spectrum with a predetermined spread amount, whereby the memory clock 122 , the system clock 126 , and the display clock 124 are obtained.
  • the clock generator that generates the non-spread spectrum clock and the clock generator that generates the spread spectrum clock so that they share the same IC that contributes curtailment of the number of parts and the area occupied on the circuitboards.
  • the three clock generators indicated in FIG. 1 are constructed using the same IC.
  • a combination of, for example, the clock generators 116 and 118 or the clock generators 120 and 118 may be constructed using the same IC.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Multimedia (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
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JP2002-177517 2002-06-18
JP2002177517A JP2004023556A (ja) 2002-06-18 2002-06-18 電子機器

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EP (1) EP1376531B1 (https=)
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KR (1) KR20040002586A (https=)
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US20110138214A1 (en) * 2009-12-04 2011-06-09 Via Technologies, Inc. Clock generator and usb module
US8892184B2 (en) 2010-10-18 2014-11-18 Siemens Medical Solutions Usa, Inc. Systems and methods for reducing interference in a dual modality imaging system

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